1. Field of the Invention
The present invention relates to an H-bridge driver having a drive signal generating circuit for generating a square-wave signal as a drive signal for driving an H-bridge that is used to drive a load from both ends thereof in a complementary fashion.
2. Description of the Prior Art
FIG. 4 shows a conventional H-bridge driver for driving a load such as the primary coil of a transformer. This H-bridge driver includes, for example, an H-bridge 400 consisting of two complementary connection circuits 300-1 and 300-2, of which each is composed of a p-channel MOS FET (hereinafter referred to as the xe2x80x9cpMOSxe2x80x9d) 301 and an n-channel MOS FET (hereinafter referred to as the xe2x80x9cnMOSxe2x80x9d) 302. Within each of the complementary connection circuits 300-1 and 300-2, the source of the pMOS 301 is connected to a supply voltage VCC, the source of the nMOS 302 is connected to ground GND, and the drains of the pMOS 301 and the nMOS 302 are connected together. In this circuit configuration, to drive the H-bridge 400, a signal P1 output from a logic circuit 100xe2x80x2 is fed through a buffer amplifier 200-1xe2x80x2 directly to the gates of the pMOS 301 and the nMOS 302 of the complementary connection circuit 300-1, and a signal P2 output from the logic circuit 100xe2x80x2, which is an inverted version of the signal P1, is fed through a buffer amplifier 200-2xe2x80x2 directly to the gates of the pMOS 301 and the nMOS 302 of the complementary connection circuit 300-2.
In this circuit configuration, let the threshold level at which the p-channel MOS FETs turn on be Vthp, and let the threshold level at which the n-channel MOS FETs turn on be Vthn Moreover, assume that the high-level voltage of the pulse signals P1 and P2 is set to be higher than VCCxe2x88x92Vthp and the low-level voltage thereof is set to be lower than Vthn. Under these conditions, when the pulse signal P1 is at the low level and the pulse signal P2 is at the high level, in the complementary connection circuit 300-1, the pMOS 301 is on and the nMOS 302 is off, and, in the complementary connection circuit 300-2, the pMOS 301 is off and the nMOS 302 is on. As a result, a current flows from the supply voltage VCC to the pMOS 301 of the complementary connection circuit 300-1, then to a load 500, then to the nMOS 302 of the complementary connection circuit 300-2, and then to ground GND. By contrast, when the pulse signal P1 is at the high level and the pulse signal P2 is at the low level, in the complementary connection circuit 300-1, the pMOS 301 is off and the nMOS 302 is on, and, in the complementary connection circuit 300-2, the pMOS 301 is on and the nMOS 302 is off. As a result, a current flows from the supply voltage VCC to the pMOS 301 of the complementary connection circuit 300-2, then to the load 500, then to the nMOS 302 of the complementary connection circuit 300-1, and then to ground GND. In this way, the load 500 is driven from both ends thereof in a complementary fashion.
However, in this conventional H-bridge driver, since the H-bridge 400 is driven by directly using the square-wave pulse signals (i.e. signals containing high-frequency components) output from the logic circuit 100xe2x80x2, the inductance component of the load 500 causes high-frequency noise of the order of tens of millivolts. For this reason, conventional H-bridge drivers are unusable in audio, visual, and similar applications.
An object of the present invention is to provide an H-bridge driver that has a drive signal generating circuit for generating a square-wave signal as a drive signal for driving an H-bridge and that permits significant reduction of the high-frequency noise caused by the inductance component of the load of the H-bridge.
To achieve the above object, according to the present invention, an H-bridge driver including a drive signal generating circuit for generating a square-wave signal as a drive signal for driving an H-bridge is provided with: a waveform shaping circuit for blunting the drive signal generated by the drive signal generating circuit to drive the H-bridge; and a control circuit for keeping the voltage on the output side of the H-bridge equal to the voltage output from the waveform shaping circuit. In this circuit configuration, a signal having a blunted version of the waveform of the drive signal for driving the H-bridge appears on the output side of the H-bridge.